Spectrometers are, broadly speaking, optical instruments which collect electromagnetic radiation from a source and resolve it into its fundamental spatial, spectral and power (or energy) components. Broadly speaking, there are two classes of spectrometers: interferometric designs; and dispersive designs. Again, broadly speaking, interferometric designs split incoming radiation into two beams and then recombine them with a distance shift across the wave front to form interference fringes. The interference patterns can be captured on film or by, for instance, a semi-conductor array detector (e.g., a charged coupled device (CCD)). The spectra of the incoming radiation is then inferred from such interference fringes via an algorithm. Sometimes an interferometer is referred to as a Fourier Transform interferometer because it is necessary to perform a Fourier Transform on the interferogram (which is the output of the instrument) in order to produce the spectra of the imaged light. Dispersive spectrometers include an optical element that has some property that varies with wavelength. The most common examples are gratings and prisms. In such spectrometers the detector directly captures the spectrum.
There are numerous interferometer designs. The basic form of the Sagnac (or common path) interferometer is illustrated in U.S. Pat. No. 4,976,542 to Smith (the “Smith patent”). Other designs include the Michelson interferometer, the Mach-Zender interferometer, the Fabry-Perot interferometer (See W. L. Wolfe, Introduction to Imaging Spectrometers, SPIE Optical Engineering Press, pp. 70-73, 1997), and a variation of the common path interferometer (Sagnac) sometimes referred to as the Barnes interferometer (see T. S. Turner Jr., et al., A Ruggedized Portable Fourier Transform Spectrometer for Hyperspectral Imaging Applications, SPIE Vol. 2585 pp 222-232.) There are also numerous dispersive spectrometers such as prism spectrometers and grating spectrometers. (See Wolfe, pp. 50-52 and 55-57).
Hyperspectral imagers have been developed for use in observing dynamic events (such as events that are changing over time or where the object is moving) with high spectral, spatial and temporal resolution over wide optical bandwidths. The “hyper” simply means that the instrument acquires a large number of spectral bands. Hyperspectral imagers also have the capability of decoupling spectral and spatial resolution. A spatially modulated Fourier transform imager can simultaneously record a complete spectrum, thus assuring spectral co-registration. Remote sensing from satellites and aircraft are among the earliest practical uses for such hyperspectral imagers.
As an illustration, in FIG. 1 a Sagnac based hyperspectral interferometric imager 11 includes fore-optics 13, a field stop 15, a common path or Sagnac interferometer 17, what is known as a Fourier lens 19, cylinder optics 21, and a detector or imager 23. (Imagers are also sometimes referred to as sensors. However, for the purpose of this application, imager will be used to refer to the detector, whether film or a semi-conductor array detector (e.g., a charged coupled device or CCD).) With such a hyperspectral instrument the object is observed through fore-optics 13 that focus the image onto field stop 15, where the width of stop 15 is used only to set one dimension of the image, the spatial resolution, not to determine the spectral resolution, a unique feature of these devices. Fore-optics 13 can take the form of custom or off-the-shelf lenses, standard or custom lens systems such as used on conventional cameras, or custom or stock telescope systems for longer imaging distances. Interferometer 17 is of the type disclosed in the Smith patent. Fourier lens 19 and cylinder optics 21 are image formation lenses.
Typical dispersive instruments include the transmissive grating spectrometer schematically illustrated in FIG. 2 and the reflective grating spectrometer schematically illustrated in FIG. 3. Spectrometer 31 includes a slit 33, a collimating lens 35, a dispersive element 37, a focusing lens 39 and a detector array 41. As illustrated, element 37 is a transmission grating. Spectrometer 51 includes a slit 53, a first mirror 55, a reflective grating 57, a second mirror 59 and a detector array 61. Instruments with reflective gratings work over a larger range of wavelengths than those with transmissive gratings.
Up until the present invention, Applicants do not believe that imagers were used with lasers in non-laboratory settings (e.g., field measurements, manufacturing applications, etc.). Thus, the application of a spectral imager to:                determine beam size on an object;        determine beam location on an object;        a determine beam parameters on an object;        determine beam-object interaction(s);        identify one or more specific spectral signatures based on beam-object interaction; and/or        determine a specific event based on detecting one or more specific spectral signatures;represents a novel and unobvious application of the technology.        